1. Field of the Invention
The present invention relates to a sheet processing apparatus that performs processing on sheets, and an image forming apparatus that is equipped with the sheet processing apparatus.
2. Description of the Related Art
In a conventional image forming apparatus such as a copying machine, a printer, and a facsimile machine, a sheet processing apparatus may comprise a sheet processing portion that supplies sheets having images formed thereon one by one into the apparatus and binds the sheets. With this sheet processing apparatus, the binding process to be performed on the sheets, such as copy sheets, on which image formation has been carried out can be omitted.
In the sheet processing apparatus disclosed in Japanese Unexamined Patent Publication No. 2004-59314, for example, sheets are discharged and stacked on an intermediate stacking portion by an intermediate roller. The end portions of the sheets stacked on the intermediate stacking portion are aligned on the intermediate stacking portion, and binding is performed by a binding device such as a stapler.
FIGS. 14 and 15 show a conventional sheet processing apparatus.
As shown in FIG. 14, this sheet processing apparatus has a trailing-end holding member 103 that prevents the top end of a subsequent sheet from running into the trailing end of a precedent sheet 104 placed on an intermediate stacking portion 101 lifted above the nip line of an intermediate roller 102, and also prevents misalignment and jamming.
This holding member 103 is provided on the downstream side of the nip position of the intermediate roller 102, and is energized in the opposite direction from the sheet conveying direction, as indicated by the arrow H. Accordingly, the position of the trailing end of the precedent sheet 104 is restricted by the lower end of the holding member 103, and is prevented from being lifted.
Therefore, the trailing end of the precedent sheet 104 is located lower than the nip line of the intermediate roller 102 before the holding member 103 rotates by the top end of the subsequent sheet. The top end of the subsequent sheet reaches a point on the downstream side deeper than the trailing end of the precedent sheet when the holding member 103 rotates. Thus, the top end of the subsequent sheet does not run into the trailing end of the precedent sheet 104.
However, in a case where each sheet is tightly curled, for example, the trailing end of a precedent sheet might lean on an alignment reference wall 105.
In that case, the holding member 103 is not energized in such a direction as to push the sheet against the sheet stacking face of the intermediate stacking portion 101. As a result, the holding member 103 cannot return to its original position due to the leaning of the precedent sheet 104, as shown in FIG. 15. The trailing end of the precedent sheet 104 cannot be restricted to a lower position than the nip line of the intermediate roller 102, and the subsequent sheet runs into the trailing end of the precedent sheet 104, causing damage or jamming of the sheets.